GB2168971A - Cephalosporin antibiotics - Google Patents

Abstract

Compounds of general formula (I'> <IMAGE> (wherein R represents a hydrogen atom or a 3- or 4-carbamoyl group; B is -S- or -SO- (???- or ???-); and R<1> is an amino or protected amino group), salts thereof and corresponding compounds having a group of formula -COOR<2> at the 4-position (where R<2> is a hydrogen atom or a carboxyl blocking group) and having an associated anion are disclosed. Processes for their preparation and pharmaceutical compositions which comprise as active ingredient one or more cephalosporin antibiotics of general formula (I') are also disclosed.

Description

SPECIFICATION Cephalosporin antibiotics This invention relates to improvements in or relating to cephalosporins. More particularly it relates to new cephalosporin compounds and derivatives thereof having valuable antibiotic activity.

The cephalosporin compounds in this specification are named with reference to "cepham" after JAmer. Chem. Soc., 1962, 84, 3400, the term "cephem" referring to the basic cepham structure with one double bond.

Cephalosporin antibiotics are widely used in the treatment of diseases caused by pathogenic bacteria inhuman beings and animals, and are especially useful in the treatment of diseases caused by bacteria which are resistant to other antibiotics such as penicillin compounds, and in the treatment of penicillin-sensitive patients. In many instances it is desirable to employ a cephalosporin antibiotic which exhibits activity against both Gram-positive and Gram-negative microorganisms, and a significant amount of research has been directed to the development of various types of broad spectrum cephalosporin antibiotics.

Thus, for example, in our British Patent Specification No. 1399086, we describe a novel class of cephalosporin antibiotics containing a 7P-(or-etherified oxyimino)-acylamido group, the oxyimino group having the syn configuration. This class of antibiotic compounds is characterised by high antibacterial activity against a range of Gram-positive and Gram-negative organisms coupled with particularly high stability to p-lactamases produced by various Gram-negative organisms.

The discovery of this class of compounds has stimulated further research in the same area in attempts to find compounds which have improved properties, for example against particular classes of organisms.

This interest is reflected in the very large numbers of patent applications which have been filed relating to cephalosporin antibiotics having particular oxyimino etherifying groups in combination with particular substituents both on the 7ss-acylamido side chain and at the 3-position of the cephalosporin nucleus.

British Patent No. 1604971 generically defines a wide range of cephalosporin antibiotics in which the 7ss-position side-chain may be selected from interalia a syn 2-(2-aminothiazol-4-yl)-2-(etherified oxyimino)acetamido group in which the etherifying group may be a substituted methyl group, although the preferred etherifying group is an unsubstituted methyl group. The 3-position group may also be selected from a large number of alternatives and a possible 3-substituent according to the generic definition is an optionally substituted pyridinium-methyl group, although no preference is expressed for such a group and there is no specific exemplification of the preparation of compounds having such a 3-substituent.

We have now discovered that by the selection of a (Z)-2-(2-aminothiazol-4-yl)-2-(etherified oxyimino)acetamido group at the 7(3-position in combination with either a pyridiniummethyl or a 3-or 4-carbamoylpyridiniummethyl group at the 3-position, and also by a selection of a thiiranylmethoxyimino group as the etherified oxyimino grouping, cephalosporin compounds having a particularly advantageous profile of activity (described in more detail below) against a wide range of commonly encountered pathogenic organisms may be obtained.

Accordingly, we provide cephalosporin antibiotics of general formula (I)

(wherein R represents a hydrogen atom or a 3-or 4-carbamoyl group), non-toxic salts and non-toxic metabolically labile esters thereof.

The compounds according to the invention are syn isomers. The syn isomeric form is defined by the configuration ofthe

group with respect to the carboxamido group. In this Specification, the syn configuration is denoted structurally as

It will be understood that since the compounds according to the invention are geometric isomers, some admixture with the corresponding anti isomer may occur. Itwill further be appreciated that in the thiiranylmethyl group, the carbon atom of the thiiranyl ring adjacent to the methyl group is chiral and may therefore exist in either R or S configuration.The invention includes within its scope all individual enantiomeric forms of the compounds of formula (I) as well as mixtures (including racemic mixtures) thereof. Itwill be understood that all intermediates possessing athiiranylmethyl group used in the preparation of compounds of formula (I) may exist either as separate enantiomers or as mixtures.

The invention also includes within its scope the solvates (especially the hydrates) of the compounds of formula (I) and of their non-toxic salts. It also includes within its scope non-toxic salts and solvates of metabolically labile esters of the compounds of formula (I). It will be appreciated that the solvates should be pharmacologically acceptable.

The compounds according to the present invention may exist in tautomericforms (for example in respect of the 2-aminothiazolyl group) and it will be understood that such tautomeric forms, e.g. the 2iminothiazolinyl form, are included within the scope of the invention.

The compounds according to the invention exhibit broad spectrum antibiotic acitvity both in vitro and in vivo. They have high activity against both Gram-positive and Gram-negative organisms, including many p-lactamase producing strains. The compounds also possess high stability to ,13-lactamases produced by a range of Gram-negative and Gram-positive organisms.

Compounds according to the invention have thus been found to exhibit high activity against a broad range of Gram-positive organisms, e.g. strains (including penicillinase-producing strains) of Staphylococcus aureus, Staphylococcus epidermidis and Streptococcus species. This is coupled with high activity against various members of the Enterobacteriaceae (e.g. strains of Escherichia coli, Klebsiellapneurnoniae, Citrobacter divers us, En terobacter cloacae, Serratia marcescens, Proteus mirabilis and indole-positive Proteus organisms such as Proteus vulgaris, Proteus morganii and Providence species), strains of Haemophilus influenzae, and Acinetobacter calcoaceticus as well as good activity against Pseudomonas species (e.g. Pseudomonas aeruginosa). This combination of high activity against Gram-positive organisms with high activity against Gram-negative organisms possessed by the compounds of the invention is unusual and particularly advantageous.

Non-toxic salt derivatives which may be formed by reaction of the carboxyl group present in the compounds of formula (I) include inorganic base salts such as alkali metal salts (e.g. sodium and potassium salts) and alkaline earth metal salts (e.g. calcium salts); amino acid salts (e.g. lysine and arginine salts); organic base salts (e.g. procaine, phenylethylbenzylamine, dibenzylethylenediamine, ethanolamine, diethanolamine and N-methylglucosamine salts). Other non-toxic salt derivatives include acid addition salts, e.g.

formed with hydrochloric, hydrobromic, sulphuric, nitric, phosphoric, formic and trifluoroacetic acids. The salts may also be in the form of resinates formed with, for example, a polystyrene resin or cross-linked polystyrene divinylbenzene copolymer resin containing amino or quaternary amino groups or sulphonic acid groups, or with a resin containing carboxyl groups, e.g. a polyacrylicacid resin. Soluble base salts (e.g.

alkali metal salts such as the sodium salt) of the compounds of formula (i) may be used in therapeutic applications because of the rapid distribution of such salts in the body upon administration. Where, however, insoluble salts of compounds (I) are desired in a particular application, e.g. for use in depot preparations, such salts may be formed in conventional manner, for example with appropriate organic amines.

Non-toxic metabolically labile ester derivatives which may be formed by esterification of the carboxyl group in the parent compound of formula (I) include acyloxyalkyl esters, e.g. loweralkanoyloxy-methyl or -ethyl esters such as acetoxy-methyl or-ethyl or pivaloyloxymethyl esters. In addition to the above ester derivatives, the present invention includes within its scope the compounds of formula (I) in the form of other physiologically acceptable equivalents, i.e. physiologically acceptable compounds which, like the metabolically labile esters, are converted in vivo into the parent antibiotic compound of formula (I).

These and other salt and ester derivatives such as the salts with toluene-p-sulphonic and methanesulphonic acids or the esters with t-butyl ordiphenylmethyl esterifying groups may be employed as intermediates in the preparation and/or purification of the present compounds of formula (I), for example in the processes described below.

It will be appreciated that the compounds of the invention are usually present in the form of a betaine containing a positively-charged pyridinium group and a carboxylate group, and therefore esters and salts of compounds of formula (I) with bases will be associated with an anion AZ to balance the positive charge on the pyridinium ring. Such an anion will also be non-toxic and may be derived from any of the acids described above which will form non-toxic salt derivatives.

A preferred compound according to the invention by virtue of its particular advantageous antibiotic activity is (6R, 7R)-7-[ (Z)-2-(2-aminothiazol-4-yl)-2-(thiiranylmethoxyimino)acetamido]-3-(1- pyridiniummethyl)-ceph-3-em-4-carboxylate and the non-toxic salts and non-toxic metabolically labile esters thereof.

The compounds of the invention may be used for treating a variety of diseases caused by pathogenic bacteria in human beings and animals, such as respiratory tract infections and urinary tract infections.

According to another embodiment of the invention we provide a process for the preparation of an antibiotic compound of general formula (I) as hereinbefore defined or a non-toxic salt or non-toxic metabolically labile ester thereof which comprises forming a compound of formula (I')

wherein R is as defined above;B is -S- or -SO- (a- or (3-); and R1 is an amino or protected amino group] or a salt thereof, or a corresponding compound having a group of formula -COOR2 at the 4-position (where R2 is a hydrogen atom or a carboxyl blocking group, e.g. the residue of an ester-forming aliphatic or araliphatic alcohol or an ester-forming phenol, silanol or stannanol, the said alcohol, phenol, silanol or stannanol preferably containing 1-20 carbon atoms)] and having an associated anion Ee such as a halide, e.g.

chloride or bromide, or trifluoroacetate anion, by (A) acylating a compound of formula (II)

(wherein R and B are as defined above) or a salt, e.g. an acid addition salt (formed with, for example, a mineral acid such as hydrochloric, hydrobromic, sulphuric, nitric or phosphoric acid or an organic acid such as methanesulphonic ortoluene-p-sulphonic acid) or an N-silyl derivative thereof, or a corresponding compound having a group of formula -COOR2 at the 4-position (where R2 is as defined above) and having an associated anion EH as defined above, with an acid of formula (III)

(wherein R1 is an amino or protected amino group), or a salt thereof or with an acylating agent corresponding thereto; or (B) reacting a compound of formula (IV)

(wherein R1 and B are as hereinbefore defined; R3 represents hydrogen or a carboxyl blocking group; and X is a replaceable residue of a nucleophile, e.g. an acetoxy or dichloroacetoxy group or a halogen atom such as chlorine, bromine or iodine) or a salt thereof, with a pyridine compound of formula (V)

(wherein R is as defined above); whereafter, if necessary and/or desired in each instance, any of the following reactions, in any appropriate sequence, are carried out: i) reduction of a compound wherein B is -SO- to form a compound wherein B is -S-, ii) conversion of a carboxyl group into a non-toxic metabolically labile ester function, iii) formation of a non-toxic salt function, iv) removal of any carboxyl blocking and/or N-protecting groups, and v) resolution, where the initial product is a mixture of enantiomers.

The above reactions i) to v) may be carried out in conventional manner.

In the processes according to the invention, preferred carboxyl blocking and N-protecting groups R1, R2 and R3 are groups which may subsequently be removed under mild conditions (i.e. those which do not cause cleavage of the thiirane or ,B-lactam ring: see for example Theadora W. Greene, "Protective Groups in Organic Synthesis" (John Wiley and Sons, 1981)).

Other reagents and conditions used in the processes according to the invention should be chosen such thatthey do not cause significant degradation of the thiirane ring.

In the above-described process (A), the starting material of formula (II) is preferably a compound wherein B is-S-. One such starting material which has been found to be particularly suitable for use in process (A) is (SR, 7P)-7-amino-3-(1 -pyridinium-methyl)ceph-3-em-4carboxylate dihydrochloride.

Acylating agents which may be employed in the preparation of compounds of formula (I) include acid halides, particularly acid chlorides or bromides. Such acylating agents may be prepared by reacting an acid (III) or a salt thereof with a halogenating agent e.g. phosphorus pentachloride, thionyl chloride or oxalyl chloride.

Acylations employing acid halides may be effected in aqueous and non-aqueous reaction media, conveniently at temperatures offrom -50 to +500C, preferably -40 to +30 C, preferably in the presence of an acid binding agent. Suitable reaction media include aqueous ketones such as aqueous acetone, aqueous alcohols such as aqueous ethanol, esters such as ethyl acetate,-halogenated hydrocarbons such as methylene chloride, amides such as dimethylacetamide, nitriles such as acetonitrile, or mixtures of two or more such solvents.Suitable acid binding agents include tertiary amines (e.g. triethylamine or dimethylaniline), inorganic bases (e.g. calcium carbonate or sodium bicarbonate), and oxiranes such as lower 1,2-alkylene oxides (e.g. ethylene oxide or propylene oxide) which bind hydrogen halide liberated in the acylatibn reaction.

Acids offormula (III) may themselves be used as acylating agents in the preparation of compounds of formula (I). Acylations employing acids (Ill) are desirably conducted in the presence of a condensing agent, for example a carbodiimide such as N,N'-dicyclohexylcarbodiimide or N-ethyl-N'-w-dimethylaminopropyl- carbodiimide; a carbonyl compound such as carbonyldiimidazole; or an isoxazolium salt such as N-ethyl-5-phenylisoxazolium perchlorate.

Acylation may also be effected with other amide-forming derivatives of acids of formula (III) such as, for example, an activated ester, a symmetrical anhydride or a mixed anhydride (e.g.formed with pivalic acid or with a haloformate, such as a lower alkylhaloformate). Mixed anhydndes may also be formed with phosphorus acids (for example phosphoric or phosphorous acids), sulphuric acid or aliphatic or aromatic sulphonic acids (for example toluene-p-sulphonic acid). Acylations using anhydrides may conveniently be effected in the presence of an acid binding agent such as those described above for acylation using acid halides. An activated ester may conveniently be formed in situ using, for example, 1-hydroxybenzotriazole in the presence of a condensing agent as set out above. Alternatively, the activated ester may be preformed.

Acylation reactions involving the free acids or their above-mentioned amide-forming derivatives are desirably effected in an anhydrous reaction medium, e.g. methylene chloride, tetrahydrofuran, dimethylformamide or acetonitrile.

An alternative method of activation is, for example, by reacting an acid of formula (III) with a solution or suspension preformed by adding a carbonyl halide, in particular oxalyl chloride or phosgene, or a phosphoryl halide such as phosphorus oxychloride to a solvent such as a halogenated hydrocarbon, for example methylene chloride, containing a lower acyl tertiary amide such as N,N-dimethylformamide.The activated form of the the acid of formula (III) may then be reacted with a 7-amino compound of formula (II) in a suitable solvent or mixture of solvents for example alcohols such as an alkanol, e.g. ethanol or industrial methylated spirits; halogenated hydrocarbons, e.g. methylene chloride; ethers, e.g. dioxan ortetrahydrofuran; esters, e.g. ethyl acetate; ketones, e.g. acetone; amides, e.g. dimethylacetamide; nitriles, e.g.

acetonitrile; water; and mixtures thereof. The acylation reaction may conveniently be effected at temperatures of from -50 to +500C, preferably -40" to +30 C, if desired in the presence of an acid binding agent, for example as described above (e.g. triethylamine).

If desired, the above acylation reactions may be carried out in the presence of a catalyst such as 4-dimethylaminopyridine.

The acids of formula (III) and acylating agents corresponding thereto may, if desired, be prepared and employed in the form of their acid addition salts. Thus, for example, acid chlorides may conveniently be employed as their hydrochloride salts, and acid bromides as their hydrobromide salts.

A pyridine compound of formula (V) may act as a nucleophile to displace a wide variety of substituents X from a cephalosporin of formula (IV). To some extent the facility of the displacement is related to the pKa of the acid HX from which the substituent is derived. Thus atoms or groups X derived from strong acids tend, in general, to be more easily displaced than atoms or groups derived from weaker acids. The facility of the displacement is also related, to some extent, to the precise character of the substituent R in the compound of formula (V).

The displacement of X by the pyridine compound of formula (V) may conveniently be effected by maintaining the reactants in solution or suspension. The reaction is advantageously effected using the pyridine compound at a mole ratio between 1:1 and 10:1.

Nucleophilic displacement reactions may conveniently be carried out on those compounds of formula (IV) wherein the substituent Xis a halogen atom or an acyloxy group, for example as discussed below.

Acyloxy groups Compounds of formula (IV) wherein Xis an acetoxy group are convenient starting materials for use in the nucleophilic displacement reaction with the pyridine compound of formula (V). Alternative starting materials in this class include compounds of formula (IV) in which Xis the residue of a substituted acetic acid e.g.

chloroacetic acid, dichloroacetic acid and trifluoroacetic acid.

Displacement reactions on compounds (IV) possessing X substituents of this class, particularly in the case where X is an acetoxy group, may be facilitated by the presence in the reaction medium of iodide or thiocyanate ions. Reactions of this type are described in more detail in British Patent Specifications Nos.

1132621 and 1171603.

The substituent X may also be derived from formic acid, a haloformic acid such as chioroformic acid, or a carbamic acid.

When using a compound of formula (IV) in which X represents an acetoxy or substituted acetoxy group, it is generally desirable that the group R3 in formula (IV) should be a hydrogen atom and that B should represent -S-. In this case, the reaction is advantageously effected in an aqeuous medium, preferably at a pH of 5 to 8, particularly 5.5 to 7.

The above-described process employing compounds offormula (IV) in which Xis the residue of a substituted acetic acid may be carried out as described in British Patent Specification No. 1241657.

When using compounds of formula (IV) in which X is an acetoxy group, the reaction is conveniently effected at a temperature of 30"C to 110 C, preferably 50 to 80"C.

Halogens Compounds of formula (IV) in which Xis a chlorine, bromine or iodine atom can also be conveniently used as starting materials in the nucleophilic displacement reaction with the pyridine compound of formula (V).

When using compounds of formula (IV) in this class, B may represent -SO- and R3 may represent a carboxyl blocking group. The reaction is conveniently effected in a non-aqueous medium which preferably comprises one or more organic solvents, advantageously of a polar nature such as ethers, e.g. dioxan or tetrahydrofuran, esters, e.g. ethyl acetate, amides, e.g. formamide and N,N-dimethylformamide, and ketones e.g. acetone. In certain cases the pyridine compound itself may be the solvent. Other suitable organic solvents are described in more detail in British Patent Specification No. No.1326531. The reaction medium should be neither extremely acidic nor extremely basic.In the case of reactions carried out on compounds of formula (IV) in which R3 is a carboxyl blocking group the 3-pyridiniummethyl product will be formed as the corresponding halide salt which may, if desired, be subjected to one or more ion exchange reactions to obtain a salt having the desired anion.

When using compounds of formula (IV) in which Xis a halogen atom as described above, the reaction is conveniently effected at a temperature of -1 O" to +50 , preferably +10' to +30 C.

The reaction product may be separated from the reaction mixture, which may contain, for example, unchanged cephalosporin starting material and other substances, by a variety of processes including recrystallisation, ionophoresis, column chromatography and use of ion-exchangers (for example by chromatography on ion-exchange resins) or macroreticular resins.

Where-a compound is obtained in which B is -SO- this may be converted into the corresponding sulphide by, for example, reduction of the corresponding acyloxysulphonium or alkoxysulphonium salt prepared in situ by reaction with e.g. acetyl chloride in the case of an acetoxysulphonium salt, reduction being effected by, for example, sodium dithionite or by iodide ion as in a solution of potassium iodide in a solvent e.g. acetic acid, acetone, tetrahydrofuran, dioxan, dimethylformamide or dimethylacetamide. The reaction may be effected at a temperature of from -20 to +50"C.

Metabolically labile ester derivatives of the compounds of formula (I) may be prepared by reacting a compound of formula (I) or a salt or protected derivative thereof with the appropriate esterifying agent such as an acyloxyalkyl halide (e.g. iodide) conveniently in an inert organic solvent such as dimethylformamide or acetone, followed, where necessary, by removal of any protecting groups.

Base salts of the compounds of formula (I) may be formed by reacting an acid of formula (I) with an appropriate base. Thus, for example, sodium or potassium salts may be prepared using the respective 2-ethylhexanoate or hydrogen carbonate salt. Acid addition salts may be prepared by reacting a compound of formula (I) or a metabolically labile ester derivative thereof with the appropriate acid.

Where a compound of formula (I) is obtained as a mixture of isomers, the syn isomer may be obtained by, for example, conventional methods such as crystallisation or chromatography. Mixtures of enantiomers, including racemic mixtures, of compounds according to the invention or intermediates therefor may be resolved using conventional means; see for example "Stereochemistry of Carbon Compounds" by E.L. Eliel (McGraw Hill, 1962) and "Tables of Resolving Agents" by S.H. Wilen.

For use as starting materials for the preparation of compounds of general formula (I) according to the invention, compounds of general formula (III) and acid halides and anhydrides corresponding thereto in their syn isomeric form or in the form of mixtures of the syn isomers and the corresponding antiisomers containing at least 90% of the syn isomer are preferably used.

Acids of formula (III) and their derivatives are themselves novel compounds. They may be prepared by etherification of a compound of formula (Vl)

(wherein R1 is as herein before defined and R4 represents hydrogen or a carboxyl blocking group) or a salt thereof, by selective reaction with a compound of general formula (VII)

(wherein T is halogen, such as chloro, bromo or iodo; sulphate; or sulphonate, such as tosylate and mesylate), followed by removal of any carboxyl blocking group R4. The carboxyl blocking group R4 used is preferably a group which may subsequently be removed under mild conditions.For example, a p-nitrobenzyl group may be employed in which case removal of the blocking group may for example be effected using sodium bicarbonate and sodium dithionite in the presence of aqueous tetrahydrofuran.

Separation, including resolution, of isomers may be effected either before or after such etherification. The etherification reaction is conveniently carried out in the presence of a base, e.g. potassium carbonate or sodium hydride, and is preferably conducted in an organic solvent, for example dimethylsulphoxide, a cyclic ether such as tetrahydrofuran or dioxan, or an N,N-disubstituted amide such as dimethylformamide. Under these conditions the configuration of the oxyimino group is substantially unchanged by the etherification reaction. When the compound of formula (VI) is employed in the form of a free acid or a salt with a base, the etherification reaction is generally carried out in the presence of a strong base, e.g., potassium t-butoxide, sufficient base being added to form a dianion. Furthermore, the reaction should be effected in the presence of a base if an acid addition salt of a compound of formula (VI) is used, the amount of base being sufficient to neutralise rapidly the acid in question.

The acids of formula (Ill) may be converted into the corresponding acid halides and anhydrides and acid addition salts by conventional methods, for example as described hereinabove, and optionally with or without previous purification.

The compounds of formula (VII) employed as starting materials may be prepared by conventional methods e.g. by reaction with thiourea in methanol. See for example, C.C.J. Culvenor, W. Davies and K.H.

Pausacker; J. Chem. Soc 1946 1050). If desired these compounds may be purified, e.g. by distillation, before further reaction.

The compounds of formula (IV) are novel and form a further feature of the invention.

Where X is a halogen (i.e. chlorine, bromine or iodine) atom in formula (IV), the compounds may be prepared in conventional manner, e.g. by halogenation of a 7ss-protected amino-3-methylceph-3-em-4carboxylic acid ester 1(3-oxide, removal of the 7ss-protecting group, acylation of the resulting 7,3amino compound to form the desired 7ss-acylamido group, e.g. in an analogous manner to process (A) above, followed by reduction of the oxide group later in the sequence. This is described in British Patent No.

1326531.

Where X in formula (IV) is an acetoxy group, such starting materials may be prepared, for example, by acylation of 7-aminocephalosporanic acid, e.g. in an analogous mannerto process (A) above. Compounds of formula (IV) in which X represents other acyloxy groups can be prepared by acylation of the corresponding 3-hydroxymethyl compounds which may be prepared for example by hydrolysis of the appropriate 3-acetoxymethyl compounds, e.g. as described for example in British Patent Specifications Nos. 1474519 and 1531212.

The starting materials of formula (II) may also be prepared in conventional manner, for example, by nucleophilic displacement of the corresponding 3-acetoxymethyl compound with the appropriate nucleophile, e.g. as described in British Patent Specification No. 1028563, or by the method described in published British Patent Application No. 2052490A.

A further method for the preparation of the starting materials of formula (II) comprises deprotecting a corresponding protected 7ss-amino compound in conventional manner, e.g. using PC15.

It should be appreciated that in some of the above transformations it may be necessary to protect any sensitive groups in the molecule of the compound in question to avoid undesirable side reactions. For example, during any of the reaction sequences referred to above it may be necessary to protect the NH2 group of the aminothiazolyl moiety, for example bytritylation, acylation (e.g. chloroacetylation or formylation), protonation or other conventional method. The protecting group may thereafter be removed in any convenient way which does not cause breakdown of the desired compound.The thiirane grouping in the oxime portion of the compounds of formulae (III) and (IV) is susceptible to cleavage for example by strong acids or bases, and it is therefore desirable to employ N-protecting groups which can be removed under mild conditions. For example, a trityl group may be removed by using an optionally halogenated carboxylic acid, e.g. acetic acid, formic acid, chloroacetic acid or trifluoroacetic acid or mixtures of such acids, optionally in the presence of methyl phenyl ether (anisole), or, in the case of a chloroacetyl group, by treatment with thiourea.

Carboxyl blocking groups used in the preparation of compounds of formula (I) or in the preparation of necessary starting materials are desirably groups which may readily be split off at a suitable stage in the reaction sequence, conveniently at the last stage. It may, however, be convenient in some instances to employ non-toxic metabolically labile carboxyl blocking groups such as acyloxy-methyl or-ethyl groups (e.g. acetoxy-methyl or -ethyl or pivaloyloxymethyl) and retain these in the final product to give an appropriate ester derivative of a compound of formula (I).

Suitable carboxyl blocking groups are well known in the art, a list of representative blocked carboxyl groups being included in British Patent No. 1399086. Preferred blocked carboxyl groups are those which may be deblocked without the use of strongly acidic conditions, for example aryl lower alkoxycarbonyl groups such as p-methoxybenzyloxycarbonyl. p-nitrobenzyloxycarbonyl and diphenylmethoxycarbonyl. The car bonyl blocking group may subsequently be removed by any of the appropriate methods disclosed in the literature; thus, for example, mild acid or base catalysed hydrolysis is applicable in many cases, as are enzymically-catalysed hydrolyses.

The antibiotic compounds of the invention may be formulated for administration in any convenient way, by analogy with other antibiotics and the invention therefore includes within its scope pharmaceutical compositions comprising one or more antibiotic compounds in accordance with the invention adapted for use in human or veterinary medicine. Such compositions may be presented for use in conventional manner with the aid of any necessary pharmaceutical carriers or excipients.

The antibiotic compounds according to the invention may, for example, be formulated for injection and may be presented in unit dose form, in ampoules, or in multi-dose containers, if necessary with an added preservative. The compositions may also take such forms as suspensions, solutions, or emulsions in oily or aqueous vehicles, and may contain formulatory agents such as suspending, stabilising and/or dispersing agents. Alternatively the active ingredient may be in powder form for reconstitution with a suitable vehicle, e.g. sterile, pyrogen-free water, before use.

If desired, such powder formulations may contain an appropriate non-toxic base in order to improve the water-solubility of the active ingredient and/or to ensure that when the powder is reconstituted with water, the pH of the resulting aqueous formulation is physiologically acceptable. Alternatively the base may be present in the water with which the powder is reconstituted. The base may be, for example, an inorganic base such as sodium carbonate, sodium bicarbonate or sodium acetate, or an organic base such as lysine or lysine acetate.

The antibiotic compounds may also, for example, be formulated as suppositories e.g. containing conventional suppository bases such as cocoa butter or other glycerides.

Compositions for veterinary medicine may, for example, be formulated as intramammary preparations in either long acting or quick-release bases.

The compositions may contain from 0.1% upwards, e.g.0.1-99% of the active material, depending on the method of administration. When the compositions comprise dosage units, each unit will preferably contain 100-3000 mg of the active ingredient e.g. 200-2000 mg. The daily dosage for adult human treatment will preferably range from 200 to 12000 mg e.g. 1000-9000 mg per day, depending inter alia on the natureofthe infection and the route and frequency of administration. In general, intravenous or intramuscular administration will be employed, for example using 400 to 4000 mg per day of the active ingredient in adult human treatment. In treating Pseudomonas infections higher daily doses may be required.It will be appreciated that in some circumstances, for example, in the treatment of neonates, smaller dosage units and daily dosages may be desirable.

The antibiotic compounds according to the invention may be administered in combination with other therapeutic agents such as antibiotics, for example penicillins or other cephalosporins.

The following Examples illustrates the invention. All temperatures are in C; DMSO is dimethylsulphoxide; EtOH is ethanol.

Intermediate 1 4-Nitrob enzyl CZ)-2-hydroxyimino-2-g2-tritylaminothiazol-4yl)-acetate A mixture of sodium (Z) -2-hydroxyimino-2-(2-tritylaminothiazol-4-yI)-acetate (63.6g) and 4-nitrobenzyl bromide (33.59) in N,N-dimethylformamide (500ml) at room temperature was stirred for 1 hour and allowed to stand for 4 days. The reaction mixture was added to water (25 1) and ethyl acetate (1.5 I). The aqueous phase was acidified to pH 1 with dilute hydrochloric acid and the two phases separated. The organic phase was cooled in an ice bath and petroleum ether (1.5 I) added. The product precipitated out of solution and filtration afforded the title compound (65.89).

v,,, (CHBr3) 3550, 3400, 1740, 1610, 1600, 1523, 1348cml; h,,, (EtOH) 261 .5nm, E: 342; Xi,f 229nm, E: 484, 264nm, [1cm 340, 270nm, E1i'c1m 324.

Intermediate 2 Preparation 1 4Nitrobenzyl (Z)--2- Thifran ylmethoxyimino-2-(24rity/aminothiazol-4-yl)acetate A mixture of chloromethyl thiirane (see C.C.J. Culvenor, W. Davies and K.H. Pausacker, J. Chem. Soc. 1946 1050) (1.9549), Intermediate 1 (3.9859) and potassium carbonate (4.159) in dimethylsulphoxide (75ml) was stirred at room temperature for 26 hours. The reaction mixture was diluted with ethyl acetate (400ml) and washed successively with water, sodium hydrogen sulphate solution, water, saturated sodium chloride solution and dried with magnesium sulphate. The solvent-was removed under reduced pressure.The crude product was purified by flash chromatography on silica gel to afford the title compound (2.79). T (CDCl3) includes 3.48 (thiazole proton), 5.73 (t,J 6Hz) 6.83 (m), 7.4-7.9(m).

Preparation 2 4-Nitrobenzyl 24hllran ylmeth ox yim in o-2-(2-tritylaminothiazol-4-y/)aceta te 2-Chloromethylthiirane (see C.C.J. Culvenor, W. Davies and K.H. Pausacker, J. Chem. Soc. 1946, 1050) (5.04ml) and potassium carbonate (89) were added to a solution of Intermediate 1 (8g) in dimethylsulphoxide (40ml). The resultant mixture was stirred at ambient temperature for 1.75 hours when it was poured into ethyl acetate (800ml) and water (100ml) and the two phases were separated. The organic phase was washed with water(100ml, 2 x 50ml),10% sodium hydrogen sulphate solution (2 x 100ml), water (100ml) and saturated brine (100ml). The ethyl acetate solution was finally dried over anhydrous magnesium sulphate and evaporated under reduced pressure to an oil.This was dried in vacuo at room temperature to yield 9.29 of the title compound.

A sample of the above foam (2g) was dissolved in ethyl acetate (5ml) and diluted 1:1 with 40/60 petroleum ether. This solution was applied to a 6 x 10cm column of Kieselgel 60 (ART 9385, 110g) packed under pressure in ethyl acetate/40:60 petroleum ether (1 :3).The column was-eluted under slight nitrogen pressure with the same solvent mixture. The fractions containing the purified compound were collected and soncentrated under reduced pressure to give 1.399 of the title compound.

vmax (CHBr3) 3400 (NH), 1746 1746 (COOR), 1528 + 1349 (Ar-NO2), 754 (Ph) cm-1.

Tvalues (CDCl3) include 1.81 and 2.44 (d,d.J=9Hz, phenyl protons); 2.75 (trityl); 3.10 (N-H); 3.50 (aminothiazol proton); 4.60 (COOCH2-); 5.72 (t,J=6Hz, O-CH2); 6.83 (m, thiiranyl methylene proton), 7.47.9 (thiiranyl methine proton).

Intermediate 3 Preparation 1 (Z)-2-Thifran ylmethoxyimino-2-(2-tritylamThoth/azoAvl)acetic acid A mixture of intermediate 2 (0.899) and sodium dithionite (2.869) in water (24ml), saturated aqueous sodium hydrogen carbonate (12ml) and tetrahydrofuran (36ml) was stirred at room temperature for 1.75 hours. The reaction mixture was added to ethyl acetate (250ml) and washed successively with sodium hydrogen sulphate solution, saturated sodium chloride solution and dried with magnesium sulphate.

Removal of solvent under vacuum afforded the title compound in quantitative yield.

T (d6-DMSO) includes 3.09 (thiazole proton), 5.62-6.2 (m) 6.84 (q, J 7Hz) 7.4-7.8(m).

Preparation 2 (Z)-2- ThiEranylmethoxyAmino-2-62-tritylaminothiazol-4-ylVacetic acid Water (140ml) and saturated sodium bicarbonate solution (70ml) were added to a solution of Intermediate 2 (5.2g) in tetrahydrofuran (210ml) under nitrogen. Sodium dithionite (16.7g) was added and the mixture was stirred at ambient temperature (21 -22 ) for 1.5 hours. The reaction was partitioned between a stirred mixture of ethyl acetate (750ml) and 10% w/w sodium hydrogen sulphate solution (300ml).The separated aqeuous phase was extracted with further ethyl acetate and the bulked organic fractions were washed with 10% w/w sodium hydrogen sulphate (75ml) and 1:1 10% sodium hydrogen sulphate solution/-saturated brine (100ml) before drying over anhydrous magnesium sulphate. The solution was concentrated under reduced pressure to a pale yellow solid which was dried in vacuo at ambient temperature to give 4.71 g of the title compound.

A 1.6g aliquot of the title compound was adsorbed onto a column of silica (lOOg) from solution in dichloromethane:methanol 8:1 v/v. Elution with the same solvent mixture allowed the isolation of a purified version of the title compound (1.1 g). T values (DMSO-d6) include 1.37 (N-H); ca 2.75 (triphenylmethyl H); 3.28 (aminothiazole H); 5.75-6.45 (-CH2-); 6.89 (thiirane ring methine H); approx. 7.35-7.9 (thiirane ring methylene, ABq, 6Hz).

Example 1 (6R, 7R)-7-[(Z)-2-(2-Aminothiazol-4-yl)-2-thiranylmethoxysmino)acetamido]-3-(1-pyridiniummethyl)ceph-3- em-4-carboxylate, hydrochloride Oxalyl chloride (0.14ml) was added to a solution of N,N-dimethylformamide (0.38ml) in methylene chloride (3.5ml) at -20 C. The resultant solution was stirred at -20 C for 10 minutes, in an ice bath for 15 minutes and then recooled to -20 C.

A solution of Intermediate 3 (0.74g) in methylene chloride (4ml) was added. The reaction mixture was stirred in an ice bath for 50 mins and then added to a stirred solution of (6R,7R)-7-amino-3-(1-pyridinium- methyl)ceph-3-em-4-carboxylate dihydrochloride dihydrate (534.6mg) in water (4.5ml), triethylamine (2.25m1) and industrial methylated spirits (18m1). The resultant mixture was stirred at room temperature for 60 minutes was then washed with water (2 x 35ml), saturated sodium chloride solution (25ml) and dried with magnesium sulphate. Removal of solvent under reduced pressure gave a solid to which formic acid (10ml) and concentrated hydrochloric acid (0.56ml) were added. The resultant mixture was stirred for 90 ninutes at room temperature and filtered. The formic acid was removed from the filtrate under reduced pressure. Trituration with acetone afforded material which was purified by chromatography on silica to afford the title compound (88mg). T(d6-DMSO) includes 0.5(d), 0.61 (d, J 8Hz), 1.40(m), 1.82(m) 4.29 and 4.87 (ABq 14Hz) 4.3(dd) 4.91 (d, JHz) hint (EtOH) 230nm, E}'ctn 197; 242nm, Ei1cm 179; 260nm, E1cm 150; 287nm, E1cm 105; 325nm, E1 ' rn 75.

Claims (13)

1. Compounds of general formula (I')

(wherein R represents a hydrogen atom or a 3-or 4-carbamoyl group; B is -S- or -SO- (o- or (3-); and R1 is an amino or protected amino group), salts thereof and corresponding compounds having a group of formula -COOR2 at the 4-position (where R2 is a hydrogen atom or a carboxyl blocking group) and having an associated anion.

2. Compounds as claimed in claim 1 having the general formula (I)

(wherein R represents a hydrogen atom or a 3-or 4- carbamoyl group), non-toxic salts, non-toxic metabolically labile esters and solvates thereof.

3. (6R,7R)-7-[(Z)-2-(2-aminothiazol-4-yl)-2-(thiiranyl methoxyimino)acetamido]-3-(1 -pyridinium-methyl) ceph-3-em-4-carboxylate, non-toxic salts, non-toxic metabolically labile esters and solvates thereof.

4. A process for the preparation of a compound as claimed in claim 1 which comprises either (A) acylating a compound of formula (II)

(wherein R and B are as defined in claim 11, or a Salt or an N-silyl derivative thereof, or a corresponding compound having a group of formula -COOP2 at the 4-position (where R2 iS a hydrogen atom) and having an associated anion, with an acid of formula (III)

(wherein R1 is an amino or protected amino group), or a salt thereof or with an acylating agent corresponding thereto; or (B) reacting a compound of formula (IV)

(wherein (R1 and B are as defined in claim 1; R3 represents hydrogen or a carboxyl blocking group; and X is a replaceable residue of a nucleophile or a halogen atom), or a salt thereof with a pyridine compound of formula (V)

(wherein R is as defined in claim 1); whereafter, if necessary and/or desired, any of the following reactions, in any appropriate sequence, are carried out: i) reduction of a compound wherein b is -SO- to form a compound wherein B is -S-, ii) conversion of a carboxyl group into a non-toxic metabolically labile ester function, iii) formation of a non-toxic salt function, iv) removal of any carboxyl blocking and/or N-protecting groups, and v) resolution, where the initial product is a mixture of enantiomers.

5. A process as claimed in claim 4 wherein (6R,7R)-7-amino -3- (1-pyridiniumethyl)ceph-3-em-4- carboxylate dihydrochloride is employed as a starting material.

6. A process as claimed in claim 4 or claim 5 wherein an acid of formula (III), a salt thereof or an acylating agent corresponding thereto is employed in the syn isomeric form or in the form of a mixture of the syn isomer and the corresponding anti-isomer containing at least 90% of the syn isomer.

7. A process as claimed in claim 4 wherein a pyridine compound of formula (V) is reacted with a compound of formula (IV), our a salt thereof art a mole ratio between 1:1 and 10:1.

8. A process as claimed in claim 4 or claim 7 wherein a compound of formula (IV) is employed in which X is a halogen atom or an acyloxy group.

9. Compounds of formula (IV) as defined in claim 4 and salts thereof.

10. Pharmaceutical compositions which comprise as active ingredients at least one compound as claimed in claim 2, in association with one or more pharmaceutical carriers and/or excipients.

11. A process as claimed in claim 4 substantially as hereinbefore described.

12. A process as claimed in claim 4 substantially as hereinbefore described with reference to the Example.

13. A pharmaceutical composition as claimed in claim 10 substantially as hereinbefore described.